The long-term objective of the proposed research is to investigate the potential regulation of expression of Streptococcus mutans genes which are important to virulence and the induction of dental caries.The particular genes to be examined are those whose products are involved in sucrose-dependent adherence and aggregation as well as in storage polymer production and breakdown. The first aim of the research is to examine the influence of the in vivo plaque environment on the expression of two S. mutans genes whose products play a role in dental caries. The methods to be used will include infection of rats with S. mutans fusion strains, establishment of colonization of the animals, and determination of chloramphenicol acetyltransferase (CAT) specific activities as a measure of in vivo expression of S. mutans virulence-associated genes. The second aim of the work is to understand how the synthesis and breakdown of fructans (fructose polymers) contribute to S. mutans pathogenicity. The experimental design includes construction of an operon fusion between the S. mutans fructosidase gene and lac as well as determination of b-galactosidase specific activities as a measure of fructosidase gene expression. Expression studies will be performed following a variety of challenges including strictly anaerobic in vitro conditions which closely resemble the environment of plaque. These experiments should begin to address the contribution of fructan synthesis and breakdown to dental caries and enamel destruction.